Nanocomposite photodetector

Abstract

A photodetector includes an anode that is transparent or partially transparent to light, a cathode and an active layer disposed between the anode and the cathode. The active layer includes a nanocomposite material that has a polymer blended with nanoparticles or organic electron trapping particles. The photodetector has a low dark current when not illuminated by light and has a high conductivity when illuminated by light, in which the light passes the anode and is absorbed by the active layer.

What is claimed is: 
     
       1. An apparatus comprising:
 a photodetector comprising:
 an anode; 
 a cathode; 
 an active layer disposed between the anode and the cathode, the active layer comprising nanoparticles that trap electrons, 
 wherein the nanoparticles comprise at least one of zinc oxide (ZnOx), titanium oxide (TiOx), tin oxide (SnOx), zinc sulfide (ZnS), iron sulfide (FeS), iron pyrite (FeS2), Ge, InAs, InSb, Pb 1-x Sn x Te, Hg 1-x Cd x Te (0≦x<1), InAsSb, InNSb, InBiTe, or InTlSb; 
 
 a first buffer layer disposed between the active layer and the anode; and 
 a second buffer layer disposed between the active layer and the cathode, in which the first buffer layer blocks conduction of electrons and the second buffer layer blocks conduction of holes to reduce a dark current through the photodetector when the photodetector is not illuminated by light. 
 
     
     
       2. The photodetector of  claim 1  in which the nanoparticles further comprise at least one of InAs/GaInSb super lattice, HgTe/CdTe super lattice, graphene quantum dots, carbon nanotube, or fullerene. 
     
     
       3. The apparatus of  claim 1  in which the active layer comprises a polymer. 
     
     
       4. The apparatus of  claim 1  in which the active layer comprises at least one of polyvinylcarbazole (PVK), poly(3-hexylthiophene) (P3HT), poly[4,8-bis-(2-ethyl-hexyl-thiophene-5-yl)-benzo[1,2-b:4,5-b′] dithiophene-2,6-diyl]-alt-[2-(2′-ethyl-hexanoyl)-thieno [3,4-b]thiophen-4,6-diyl (PBDTTT-CT), phthalocyanine complex, a porphyrin complex, a polythiophene (PT), a derivative of polythiophene, a polycarbazole, a derivative of polycarbazole, a poly(p-phenylene vinylene) (PPV), a derivative of poly(p-phenylene vinylene), a polyfluorene (PF), a derivative of polyfluorene, a cyclopentadithiophene-based polymer, a benzodithiophene (BDT)-based polymer, a polythiophene, a derivative of polythiophene, a polycarbazole, a derivative of polycarbazole, poly(3-octylthiophene) (P3OT), poly(3-hexyloxythiophene) (P3DOT), poly(3-methylthiophene) (PMeT), poly(3-dodecylthiophene) (P3DDT), poly(3-dodecylthienylenevinylene) (PDDTV), poly(3,3 dialkylquarterthiophene) (PQT), poly-dioctyl-fluorene-co-bithiophene (F8T2), poly-(2,5,-bis(3-alkylthiophene-2-yl)thieno[3,2-b′]thiophene) (PBTTT-C12), poly[2,7-(9,9′-dihexylfluorene)-alt-2,3-dimethyl-5,7-dithien-2-yl-2,1,3-benzothiadiazole] (PFDDTBT), poly{[2,7-(9,9-bis-(2-ethylhexyl)-fluorene)]-alt-[5,5-(4,7-di-20-thienyl-2,1,3-benzothiadiazole)]} (BisEH-PFDTBT), poly{[2,7-(9,9-bis-(3,7-dimethyl-octyl)-fluorene)]-alt-[5,5-(4,7-di-20-thienyl-2,1,3-benzothiadiazole)]} (BisDMO-PFDTBT), poly[N-9″-hepta-decanyl-2,7-carbazole-alt-5,5-(4′,7′-di-2-thienyl-2′,1′,3′-benzothiadiazole)] (PCDTBT), or a combination of two or more of the above materials. 
     
     
       5. The apparatus of  claim 1  in which the anode comprises at least one of indium tin oxide (ITO), fluorine-doped tin oxide (FTO), aluminum-doped zinc oxide (AZO), antimony-tin mixed oxide (ATO), a conductive polymer, a network of metal nanowire, a network of carbon nanowire, nanotube, nanosheet, nanorod, carbon nanotube, silver nanowire, or graphene. 
     
     
       6. The apparatus of  claim 1  in which the cathode comprises at least one of aluminum, calcium, magnesium, lithium, sodium, potassium, strontium, cesium, barium, iron, cobalt, nickel, copper, silver, zinc, tin, samarium, ytterbium, chromium, gold, graphene, an alkali metal fluoride, an alkaline-earth metal fluoride, an alkali metal chloride, an alkaline-earth metal chloride, an alkali metal oxide, an alkaline-earth metal oxide, a metal carbonate, a metal acetate, or a combination of two or more of the above materials. 
     
     
       7. The apparatus of  claim 1  in which the first buffer layer comprises at least one of an organic materials or self-assembled monolayers (SAMs). 
     
     
       8. The apparatus of  claim 1  in which the first buffer layer comprises at least one of poly(3,4-ethylenedioxithiophene) (PEDOT) doped with poly(styrene sulfonicacid) (PSS), 4,4′-bis[(ptrichlorosilylpropylphenyl)phenylamino]biphenyl (TPD-Si2), poly(3-hexyl-2,5-thienylene vinylene) (P3HTV) and C60, copper phthalocyanine (CuPc), poly[3,4-(1hydroxymethyl) ethylenedioxythiophene] (PHEDOT), n-dodecylbenzenesulfonic acid/hydrochloric acid-doped poly(aniline) nanotubes (a-PANIN)s, poly(styrenesulfonic acid)-graft-poly(aniline) (PSSA-g-PANI), poly[(9,9-dioctylfluorene)-co-N-(4-(1-methylpropyl)phenyl)diphenylamine] (PFT), 4,4′-bis[(p-trichlorosilylpropylphenyl) phenylamino]biphenyl (TSPP), 5,5′-bis[(p-trichlorosilylpropylphenyl) phenylamino]-2,20-bithiophene (TSPT), N-propyltriethoxysilane, 3,3,3-trifluoropropyltrichlorosilane or 3-aminopropyltriethoxysilane, V 2 O 5 , VOx, MoO 3 , WO 3 , ReO 3 , NiOx, AgOx/PEDOT:PSS, Cu 2 O, CuSCN/P3HT, or Au nanoparticles. 
     
     
       9. The apparatus of  claim 1  in which the second buffer layer comprises at least one of an alkali metal compound, a metal oxide, an organic material, or self-assembled monolayers (SAMs). 
     
     
       10. The apparatus of  claim 1  in which the second buffer layer comprises at least one of LiF, CsF, LiCoO 2 , Cs 2 CO 3 , TiOx, TiO 2  nanorods (NRs), ZnO, ZnO nanorods (NRs), ZnO nanoparticles (NPs), ZnO, Al 2 O 3 , CaO, bathocuproine (BCP), copper phthalocyanine (CuPc), pentacene, pyronin B, pentadecafluorooctyl phenyl-C60-butyrate (F-PCBM), C60, C60/LiF, ZnO NRs/PCBM, ZnO/cross-linked fullerene derivative (C-PCBSD), single walled carbon nanotubes (SWCNT), poly(ethylene glycol) (PEG), poly(dimethylsiloxane-block-methyl methacrylate) (PDMS-b-PMMA), polar polyfluorene (PF-EP), polyfluorene bearing lateral amino groups (PFN), polyfluorene bearing quaternary ammonium groups in the side chains (WPF-oxy-F), polyfluorene bearing quaternary ammonium groups in the side chains (WPF-6-oxy-F), fluorene alternating and random copolymer bearing cationic groups in the alkyl side chains (PFNBr-DBT15), fluorene alternating and random copolymer bearing cationic groups in the alkyl side chains (PFPNBr), or poly(ethylene oxide) (PEO). 
     
     
       11. The apparatus of  claim 1  in which the active layer absorbs light having a wavelength in a first predetermined range. 
     
     
       12. The apparatus of  claim 11  in which the anode is transparent or partially transparent to light having a wavelength in a second predetermined range, the second predetermined range overlapping the first predetermined range in a third predetermined range. 
     
     
       13. The apparatus of  claim 12  in which the photodetector has a high resistivity when not illuminated by light and has a low resistivity when illuminated by light having a wavelength in the third predetermined range. 
     
     
       14. An apparatus comprising:
 a photodetector array comprising:
 a plurality of anode lines that are individually selectable; 
 a plurality of cathode lines that are individually selectable; and 
 an active layer disposed between the anode lines and cathode lines, the active layer comprising nanoparticles that trap electrons, in which each intersection of one of the anode lines and one of the cathode lines form an individually selectable photodetector,
 wherein the nanoparticles comprise at least one of zinc oxide (ZnOx), titanium oxide (TiOx), tin oxide (SnOx), zinc sulfide (ZnS), iron sulfide (FeS), iron pyrite (FeS2), Ge, InAs, InSb, Pb 1-x Sn x Te, Hg 1-x Cd x Te (0≦x<1), InAsSb, InNSb, InBiTe, or InTlSb. 
 
 
 
     
     
       15. The apparatus of  claim 14 , comprising:
 a first buffer layer disposed between the active layer and the anode lines; and 
 a second buffer layer disposed between the active layer and the cathode lines, the first buffer layer having a higher hole conductivity compared to that of the second buffer layer, the second buffer layer having a higher electron conductivity compared to that of the first buffer layer. 
 
     
     
       16. The apparatus of  claim 14 , comprising a controller configured to receive an address signal and select one of the photodetectors based on the address signal. 
     
     
       17. The photodetector array of  claim 14  in which the nanoparticles comprise at least one of InAs/GaInSb super lattice, HgTe/CdTe super lattice, graphene quantum dots, carbon nanotube, or fullerene. 
     
     
       18. The apparatus of  claim 14  in which the active layer absorbs light having a wavelength in a first predetermined range. 
     
     
       19. The apparatus of  claim 14  in which the anode lines are transparent or partially transparent to light having a wavelength in a second predetermined range, the second predetermined range overlapping the first predetermined range in a third predetermined range. 
     
     
       20. The apparatus of  claim 14  in which each photodetector has a high resistivity when not illuminated by light and has a low resistivity when illuminated by light having a wavelength in the third predetermined range. 
     
     
       21. An apparatus comprising:
 a photodetector comprising:
 an anode that is transparent or partially transparent to light having a wavelength in a first predetermined range; 
 a cathode; and 
 an active layer disposed between the anode and the cathode, in which the active layer comprises nanoparticles that trap electrons, and the active layer absorbs light having a wavelength in a second predetermined range, the second predetermined range overlapping the first predetermined range in a third predetermined range,
 wherein the nanoparticles comprise at least one of zinc oxide (ZnOx), titanium oxide (TiOx), tin oxide (SnOx), zinc sulfide (ZnS), iron sulfide (FeS), iron pyrite (FeS2), Ge, InAs, InSb, Pb 1-x Sn x Te, Hg 1-x Cd x Te (0≦x<1), InAsSb, InNSb, InBiTe, or InTlSb; 
 
 
 wherein the photodetector has a high resistivity when not illuminated by light and has a low resistivity when illuminated by light having a wavelength in the third predetermined range. 
 
     
     
       22. The apparatus of  claim 21 , comprising
 a first buffer layer disposed between the active layer and the anode; and 
 a second buffer layer disposed between the active layer and the cathode, the first buffer layer having a higher hole conductivity compared to that of the second buffer layer, the second buffer layer having a higher electron conductivity compared to that of the first buffer layer. 
 
     
     
       23. The apparatus of  claim 22  in which the first buffer layer comprises at least one of an organic materials or self-assembled monolayers (SAMs). 
     
     
       24. The apparatus of  claim 22  in which the first buffer layer comprises at least one of poly(3,4-ethylenedioxithiophene) (PEDOT) doped with poly(styrene sulfonicacid) (PSS), 4,4′-bis[(ptrichlorosilylpropylphenyl)phenylamino]biphenyl (TPD-Si2), poly(3-hexyl-2,5-thienylene vinylene) (P3HTV) and C60, copper phthalocyanine (CuPc), poly[3,4-(1hydroxymethyl) ethylenedioxythiophene] (PHEDOT), n-dodecylbenzenesulfonic acid/hydrochloric acid-doped poly(aniline) nanotubes (a-PANIN)s, poly(styrenesulfonic acid)-graft-poly(aniline) (PSSA-g-PANI), poly[(9,9-dioctylfluorene)-co-N-(4-(1-methylpropyl)phenyl)diphenylamine] (PFT), 4,4′-bis[(p-trichlorosilylpropylphenyl) phenylamino]biphenyl (TSPP), 5,5′-bis[(p-trichlorosilylpropylphenyl) phenylamino]-2,20-bithiophene (TSPT), N-propyltriethoxysilane, 3,3,3-trifluoropropyltrichlorosilane or 3-aminopropyltriethoxysilane, V 2 O 5 , VOx, MoO 3 , WO 3 , ReO 3 , NiOx, AgOx/PEDOT:PSS, Cu 2 O, CuSCN/P3HT, or Au nanoparticles. 
     
     
       25. The apparatus of  claim 22  in which the second buffer layer comprises at least one of an alkali metal compound, a metal oxide, an organic material, or self-assembled monolayers (SAMs). 
     
     
       26. The apparatus of  claim 22  in which the second buffer layer comprises at least one of LiF, CsF, LiCoO 2 , Cs 2 CO 3 , TiOx, TiO 2  nanorods (NRs), ZnO, ZnO nanorods (NRs), ZnO nanoparticles (NPs), ZnO, Al 2 O 3 , CaO, bathocuproine (BCP), copper phthalocyanine (CuPc), pentacene, pyronin B, pentadecafluorooctyl phenyl-C60-butyrate (F-PCBM), C60, C60/LiF, ZnO NRs/PCBM, ZnO/cross-linked fullerene derivative (C-PCBSD), single walled carbon nanotubes (SWCNT), poly(ethylene glycol) (PEG), poly(dimethylsiloxane-block-methyl methacrylate) (PDMS-b-PMMA), polar polyfluorene (PF-EP), polyfluorene bearing lateral amino groups (PFN), polyfluorene bearing quaternary ammonium groups in the side chains (WPF-oxy-F), polyfluorene bearing quaternary ammonium groups in the side chains (WPF-6-oxy-F), fluorene alternating and random copolymer bearing cationic groups in the alkyl side chains (PFNBr-DBT15), fluorene alternating and random copolymer bearing cationic groups in the alkyl side chains (PFPNBr), or poly(ethylene oxide) (PEO). 
     
     
       27. The photodetector of  claim 21  in which the nanoparticles further comprise at least one of InAs/GaInSb super lattice, HgTe/CdTe super lattice, graphene quantum dots, carbon nanotube, or fullerene. 
     
     
       28. The apparatus of  claim 21  in which the active layer comprises a polymer. 
     
     
       29. The apparatus of  claim 21  in which the active layer comprises at least one of polyvinylcarbazole (PVK), poly(3-hexylthiophene) (P3HT), poly[4,8-bis-(2-ethyl-hexyl-thiophene-5-yl)-benzo[1,2-b:4,5-b′] dithiophene-2,6-diyl]-alt-[2-(2′-ethyl-hexanoyl)-thieno [3,4-b]thiophen-4,6-diyl (PBDTTT-CT), phthalocyanine complex, a porphyrin complex, a polythiophene (PT), a derivative of polythiophene, a polycarbazole, a derivative of polycarbazole, a poly(p-phenylene vinylene) (PPV), a derivative of poly(p-phenylene vinylene), a polyfluorene (PF), a derivative of polyfluorene, a cyclopentadithiophene-based polymer, a benzodithiophene (BDT)-based polymer, a polythiophene, a derivative of polythiophene, a polycarbazole, a derivative of polycarbazole, poly(3-octylthiophene) (P3OT), poly(3-hexyloxythiophene) (P3DOT), poly(3-methylthiophene) (PMeT), poly(3-dodecylthiophene) (P3DDT), poly(3-dodecylthienylenevinylene) (PDDTV), poly(3,3 dialkylquarterthiophene) (PQT), poly-dioctyl-fluorene-co-bithiophene (F8T2), poly-(2,5,-bis(3-alkylthiophene-2-yl)thieno[3,2-b]thiophene) (PBTTT-C12), poly[2,7-(9,9′-dihexylfluorene)-alt-2,3-dimethyl-5,7-dithien-2-yl-2,1,3-benzothiadiazole] (PFDDTBT), poly{[2,7-(9,9-bis-(2-ethylhexyl)-fluorene)]-alt-[5,5-(4,7-di-20-thienyl-2,1,3-benzothiadiazole)]} (BisEH-PFDTBT), poly{[2,7-(9,9-bis-(3,7-dimethyl-octyl)-fluorene)]-alt-[5,5-(4,7-di-20-thienyl-2,1,3-benzothiadiazole)]} (BisDMO-PFDTBT), poly[N-9″-hepta-decanyl-2,7-carbazole-alt-5,5-(4′,7′-di-2-thienyl-2′,1′,3′-benzothiadiazole)] (PCDTBT), or a combination of two or more of the above materials. 
     
     
       30. The apparatus of  claim 21  in which the anode comprises at least one of indium tin oxide (ITO), fluorine-doped tin oxide (FTO), aluminum-doped zinc oxide (AZO), antimony-tin mixed oxide (ATO), a conductive polymer, a network of metal nanowire, a network of carbon nanowire, nanotube, nanosheet, nanorod, carbon nanotube, silver nanowire, or graphene. 
     
     
       31. The apparatus of  claim 21  in which the cathode comprises at least one of aluminum, calcium, magnesium, lithium, sodium, potassium, strontium, cesium, barium, iron, cobalt, nickel, copper, silver, zinc, tin, samarium, ytterbium, chromium, gold, graphene, an alkali metal fluoride, an alkaline-earth metal fluoride, an alkali metal chloride, an alkaline-earth metal chloride, an alkali metal oxide, an alkaline-earth metal oxide, a metal carbonate, a metal acetate, or a combination of two or more of the above materials. 
     
     
       32. A method comprising:
 applying a bias voltage across a cathode and an anode of a photodetector, the photodetector having an active layer disposed between the cathode and the anode, the active layer comprising nanoparticles,
 wherein the nanoparticles comprise at least one of zinc oxide (ZnOx), titanium oxide (TiOx), tin oxide (SnOx), zinc (ZnS), iron pyrite (FeS), iron pyrite (FeS2), Ge, InAs, InSb, Pb 1-x Sn x Te, Hg 1-x Cd x Te (0≦x<1), InAsSb, InNSb, InBiTe, or InTlSb; and 
 
 detecting light by transmitting the light through the anode to the active layer, absorbing the light in the active layer, and increasing a current flowing through the photodetector. 
 
     
     
       33. The method of  claim 32 , comprising reducing a dark current of the photodetector when there is no light by using a first buffer layer to block conduction of electrons, the first buffer layer being disposed between the active layer and the anode, and using a second buffer layer to block conduction of holes, the second buffer layer being disposed between the active layer and the cathode. 
     
     
       34. The method of  claim 32 , comprising upon absorbing light at the active layer, producing electrons and holes from an interaction of the light and materials in the active layer, and trapping the electrons using the nanoparticles. 
     
     
       35. A method comprising:
 applying a bias voltage across a cathode and an anode of a photodetector, the photodetector having an active layer disposed between the cathode and the anode, the active layer comprising nanoparticles,
 wherein the nanoparticles comprise at least one of zinc oxide (ZnOx), titanium oxide (TiOx), tin oxide (SnOx), zinc sulfide (ZnS), iron sulfide (FeS), iron pyrite (FeS2), Ge, InAs, InSb, Pb 1-x Sn x Te, Hg 1-x Cd x Te (0≦x<1), InAsSb, InNSb, InBiTe, or InTlSb; 
 
 when the photodetector is not illuminated by light, operating the photodetector in a first mode comparable to a photodiode having a rectifying Schottky contact; and 
 when the photodetector is illuminated by light, operating the photodetector in a second mode comparable to a photoconductor having an Ohmic contact. 
 
     
     
       36. The method of  claim 35 , comprising, when the photodetector is illuminated by light, transmitting the light through the anode to the active layer, absorbing the light in the active layer, and increasing a current flowing through the photodetector. 
     
     
       37. The method of  claim 35 , comprising, when the photodetector is not illuminated by light, reducing a dark current of the photodetector by using a first buffer layer to block conduction of electrons, the first buffer layer being disposed between the active layer and the anode, and using a second buffer layer to block conduction of holes, the second buffer layer being disposed between the active layer and the cathode. 
     
     
       38. The apparatus of  claim 1 , further comprising a voltage source to provide a bias voltage across the anode and the cathode of the photodetector. 
     
     
       39. The apparatus of  claim 14 , further comprising a voltage source to provide a bias voltage across a selected one of the anode lines and a selected one of the cathode lines of the photodetector array. 
     
     
       40. The apparatus of  claim 21 , further comprising a voltage source to provide a bias voltage across the anode and the cathode of the photodetector. 
     
     
       41. An apparatus comprising:
 a photodetector comprising:
 an anode; 
 a cathode; 
 an active layer disposed between the anode and the cathode, the active layer comprising electron trapping particles; 
 a first buffer layer disposed between the active layer and the anode, the first buffer layer comprises at least one of 4,4′-bis[(ptrichlorosilylpropylphenyl)phenylamino]biphenyl (TPD-Si2), poly(3-hexyl-2,5-thienylene vinylene) (P3HTV) and C60, copper phthalocyanine (CuPc), poly[3,4-(1hydroxymethyl) ethylenedioxythiophene] (PHEDOT), n-dodecylbenzenesulfonic acid/hydrochloric acid-doped poly(aniline) nanotubes (a-PANIN)s, poly(styrenesulfonic acid)-graft-poly(aniline) (PSSA-g-PANI), poly[(9,9-dioctylfluorene)-co-N-(4-(1-methylpropyl)phenyl)diphenylamine] (PFT), 4,4′-bis[(p-trichlorosilylpropylphenyl) phenylamino]biphenyl (TSPP), 5,5′-bis[(p-trichlorosilylpropylphenyl) phenylamino]-2,20-bithiophene (TSPT), N-propyltriethoxysilane, 3,3,3-trifluoropropyltrichlorosilane or 3-aminopropyltriethoxysilane, V 2 O 5 , VOx, MoO 3 , WO 3 , ReO 3 , NiOx, Cu 2 O, CuSCN/P3HT, or Au nanoparticles; and 
 a second buffer layer disposed between the active layer and the cathode, in which the first buffer layer blocks conduction of electrons and the second buffer layer blocks conduction of holes to reduce a dark current through the photodetector when the photodetector is not illuminated by light. 
 
 
     
     
       42. The apparatus of  claim 41  in which the active layer of the photodetector comprises nanoparticles that trap electrons. 
     
     
       43. The apparatus of  claim 41 , further comprising a voltage source to provide a bias voltage across the anode and the cathode of the photodetector. 
     
     
       44. The apparatus of  claim 41  in which the nanoparticles comprise at least one of zinc oxide (ZnOx), titanium oxide (TiOx), tin oxide (SnOx), zinc sulfide (ZnS), iron sulfide (FeS), iron pyrite (FeS2), Ge, InAs, InSb, Pb 1-x Sn x Te, Hg 1-x Cd x Te, InAsSb, InNSb, InBiTe, or InTlSb. 
     
     
       45. An apparatus comprising:
 a photodetector comprising:
 an anode; 
 a cathode; 
 an active layer disposed between the anode and the cathode, the active layer comprising electron trapping particles; 
 a first buffer layer disposed between the active layer and the anode; and 
 a second buffer layer disposed between the active layer and the cathode, in which the first buffer layer blocks conduction of electrons and the second buffer layer blocks conduction of holes to reduce a dark current through the photodetector when the photodetector is not illuminated by light, wherein the second buffer layer comprises at least one of LiF, LiCoO 2 , TiOx, TiO 2  nanorods (NRs), ZnO, ZnO nanorods (NRs), ZnO nanoparticles (NPs), ZnO, Al 2 O 3 , CaO, bathocuproine (BCP), copper phthalocyanine (CuPc), pentacene, pyronin B, pentadecafluorooctyl phenyl-C60-butyrate (F-PCBM), C60, C60/LiF, ZnO NRs/PCBM, ZnO/cross-linked fullerene derivative (C-PCBSD), single walled carbon nanotubes (SWCNT), poly(ethylene glycol) (PEG), poly(dimethylsiloxane-block-methyl methacrylate) (PDMS-b-PMMA), polar polyfluorene (PF-EP), polyfluorene bearing lateral amino groups (PFN), polyfluorene bearing quaternary ammonium groups in the side chains (WPF-oxy-F), polyfluorene bearing quaternary ammonium groups in the side chains (WPF-6-oxy-F), fluorene alternating and random copolymer bearing cationic groups in the alkyl side chains (PFNBr-DBT15), fluorene alternating and random copolymer bearing cationic groups in the alkyl side chains (PFPNBr), or poly(ethylene oxide) (PEO). 
 
 
     
     
       46. The apparatus of  claim 45  in which the active layer of the photodetector comprises nanoparticles that trap electrons. 
     
     
       47. The apparatus of  claim 45 , further comprising a voltage source to provide a bias voltage across the anode and the cathode of the photodetector. 
     
     
       48. The apparatus of  claim 45  in which the nanoparticles comprise at least one of zinc oxide (ZnOx), titanium oxide (TiOx), tin oxide (SnOx), zinc sulfide (ZnS), iron sulfide (FeS), iron pyrite (FeS2), Ge, InAs, InSb, Pb 1-x Sn x Te, Hg 1-x Cd x Te, InAsSb, InNSb, InBiTe, or InTlSb.